Mechanochemical functionalization of silicon

ABSTRACT

The mechanochemically functionalizing silicon nanoparticles and the functionalized silicon nanoparticles are described. The processes include applying shear forces to silicon metal the presence of an alkane and thereby functionalizing the silicon with an alkyl-functionalization. The resulting product includes a plurality of silicon nanoparticles each carrying an alkyl-functionalization derived from an alkane.

CROSS-REFERENCE TO RELATED APPLICATIONS

This disclosure claims the benefit of priority to U.S. Application No.62/744,424, filed 11 Oct. 2018, which is incorporated herein in itsentirety.

FIELD OF THE INVENTION

Embodiments of the present invention generally relate to themechanochemical modification of the surface of silicon metal.

BACKGROUND

Mechanochemical processes are those where an initial step in thechemical process is the breakage of atomic bonding by a function ofmechanical force. While early studies on mechanochemical systems thoughtthat the process was a conversion of mechanical into chemical energy,work developed since the 1960s has shown the nature of the process to bedirectly connected to the cleavage of chemical bonds and therearrangement of the cleaved parts.

SUMMARY

A first embodiment is a process of mechanochemically functionalizingsilicon nanoparticles with an alkane, the process can include repeatedlyapplying sufficient shear forces to silicon metal in the presence of analkane thereby mechanochemically functionalizing the silicon andproviding an alkyl-functionalization on the surface of the silicon; andcontinuing to apply the shear forces to the silicon in the presence ofthe alkane until the silicon metal is reduced to a plurality offunctionalized silicon nanoparticles.

A second embodiment is a process that can include repeatedly applyingsufficient shear forces to silicon metal in the presence of an admixtureof an alkane and an alkene thereby mechanochemically functionalizing thesilicon and providing a functionalization on the surface of the silicon;and continuing to apply the shear forces to the silicon in the presenceof the alkane and the alkene until the silicon metal is reduced to aplurality of functionalized silicon nanoparticles.

A third embodiment is a process that includes shearing silicon metalthereby exposing a silicon surface having a Miller index other than a(111) plane or a (100) plane, the silicon surface carrying at least onesilicon radical; where the silicon radical is of sufficient energy toreact with an alkane; mechanochemically functionalizing the siliconsurface by reacting the silicon radical with an organic coating agent,thereby covalently bonding the organic coating agent to the siliconsurface.

A fourth embodiment is a material that can include a plurality ofsilicon nanoparticles each carrying an alkyl-functionalization derivedfrom an alkane.

BRIEF DESCRIPTION OF THE FIGURES

For a more complete understanding of the disclosure, reference should bemade to the following detailed description and accompanying drawingfigures wherein:

FIG. 1 is a plot of FTIR data from the product of the herein describedshear process;

FIG. 2 is a comparative plot of FTIR data from an impact only system asdescribed in U.S. Pat. No. 7,883,995;

FIG. 3 is a SEM image of the herein disclosed product; and

FIG. 4 is a TEM image of the herein disclosed product.

While specific embodiments are illustrated in the figures, with theunderstanding that the disclosure is intended to be illustrative, theseembodiments are not intended to limit the invention described andillustrated herein.

DETAILED DESCRIPTION

Objects, features, and advantages of the present invention will becomeapparent from the following detailed description. It should beunderstood, however, that the detailed description and the specificexamples, while indicating specific embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

Herein, the use of the word “a” or “an” when used in conjunction withthe term “comprising” in the claims and/or the specification may mean“one,” but it is also consistent with the meaning of “one or more,” “atleast one,” and “one or more than one.” The term “about” means, ingeneral, the stated value plus or minus 5%. The use of the term “or” inthe claims is used to mean “and/or” unless explicitly indicated to referto alternatives only or the alternative are mutually exclusive, althoughthe disclosure supports a definition that refers to only alternativesand “and/or.”

Herein are provided processes for and the products of themechanochemical functionalization of silicon surfaces by an alkane.Preferably, the mechanochemical functionalization of nanocrystallinesilicon surfaces by an alkane. As used herein, mechanochemical meanschemical processes initiated by the physical (mechanical) breakage ofbonds, in some examples the physical breakage yields radicals that canrecombine or carry out other reactions. As used herein nanocrystalline,nanocrystals, and nanoparticles refer to materials, crystals, orparticles having dimensions on a nanometer scale, as crystal domains area feature of this disclosure, crystal domains in nanocrystallinematerial, nanocrystals, and nanoparticles can have dimensions up to thedimensions of the respective material, crystal, or particles. When acrystal domain is on the same order as, for example, a nanocrystal, thenthe nanocrystal is single-crystalline.

In a first embodiment, the mechanochemically functionalizing siliconnanoparticles with an alkane includes repeatedly applying sufficientshear forces to silicon metal in the presence of an alkane. Herein, thesufficiency of the shear forces are determined by the reduction in thesize of the silicon metal, that is, the mechanical size reduction in thesilicon metal in the presence of the alkane. In one instance, asufficient shear force is a shear force that mechanically shears singlecrystalline silicon. In another instance, a sufficient shear force is ashear force that mechanically shears polycrystalline silicon. Thesilicon is thereby mechanochemically functionalized and analkyl-functionalization is provided on the surface of the silicon. Theprocess further includes continuing to apply the shear forces to thesilicon in the presence of the alkane until the silicon metal is reducedto a plurality of functionalized silicon nanoparticles.

In one instance, the applied forces are impact and shear forces. As usedherein, impact and shear forces differ in the symmetry of the force asapplied to a solid. Impact or compressive force is analogous toindentation or collision between the solid and the object applying theforce. That is, the impact force is typically a compressive forceapplied to the material and the mechanical breakage of the materialpropagates via a cleavage plane (in Si this it typically along a (111)plane). In one instance, the impact force is the aligned forces of twoexternal bodies acting on the material. Alternatively, the shear forceis the unaligned forces which separate the material into different partsin inverse directions. Importantly, this embodiment fails to provide thefunctionalization of the silicon nanoparticles if the silicon metal isreduced in size by impact forces alone.

In another instance, the mechanochemical functionalization of thesilicon includes shearing the silicon metal to expose silicon radicalson a shear surface and then reacting the silicon radicals with thealkane. Preferably, the silicon is sheared to expose a shear plane thatincludes silicon radicals. Then, prior to the reorganization of thesilicon surface or other reactions, the silicon radicals react with thealkane. In one example, a silicon radical reacts with the alkane bycleaving a H—C and extracting a hydrogen radical from the alkane chain,thereby forming a silicon-hydride and leaving a carbon radical. Thiscarbon radical can then react with a different silicon radical therebyproviding alkane-functionalization of the silicon surface. In anotherexample, the silicon radical reacts with the alkane by cleaving a C—Cbond and forming a silicon alkyl functionalization and leaving a carbonradical that, then, can react with a second silicon radical. In anotherexample, the shearing of the silicon metal provides a shear plane thatis oriented between the (113) and (114) planes, that is, the shear planeis inclined relative to the silicon (111) plane. In still anotherexample, the shear plane is not a silicon (111) plane. In yet anotherinstance, the mechanochemical functionalization of the silicon includesfracturing the silicon metal to expose silicon radicals on a fracturesurface. In one example, the fracturing of the silicon metal provides afracture plane that is primarily aligned along the silicon (111) plane.

In still another instance, the silicon metal is reduced to a pluralityof functionalized silicon nanoparticles having a d₉₀ of less than about350 nm. Preferably, the functionalized silicon nanoparticles has a d₉₀of less than about 300 nm. Even more preferably, the d₉₀ is less thanabout 250 nm.

Preferably, the shear forces are applied to the silicon metal in thepresence of a liquid alkane. Notably, the application of shear forcesadds heat to any system and the alkane can be solid at room temperature,only to melt as the shear forces add heat to the system. In anotherinstance, the shear forces are applied to the silicon metal at atemperature above the melting point of the alkane. That is, any devicecarrying the silicon and the alkane can be heated to a temperature abovethe melting point of the alkane or held at a temperature above themelting point of the alkane. More preferably, the reaction is cooled tomaintain a temperature that is above the melting point of the alkane,wherein the cooling and the heating by the application of the shearforces equilibrate to a selected temperature. In one example, the shearforces are applied at a temperature in the range of about 5-40° C.,about 5-25° C., or about 5-20° C., with the necessary heating or coolingto maintain said temperature.

In another instance, the alkane can have a molecular formula ofC_(x)H₂x₊₂ wherein x is in the range of 4 to about 25. Preferably, x isin the range of 5-20, more preferably in the range of 6-18, and evenmore preferably in the range of 6-12. Herein, the alkane can be liner(n-alkane), branched (single or multiple branches), cyclic, or acombination thereof. In one preferable example, the alkane is linear. Inanother preferable example, the alkane is branched. In still anotherinstance, the alkane can carry a functional group wherein, preferably,the functional group does not include a heteroatom that is free of adirect bond to a hydrogen atom. Examples of functional groups includeethers, trialkyl-amines, imides, and tetraalkyl-silanes. Preferably, thefunctional groups are fully saturated and do not include any doublebonds (e.g., excluding ketones, esters, and imides).

In yet another instance, the functionalized silicon nanoparticles arepolycrystalline silicon nanocrystals. As used herein, a polycrystallinesilicon nanocrystal is a discrete silicon nanocrystal that has more thanone crystal domain. The domains can be of the same crystal structure anddisplay discontinuous domains, or the domains can be of differentcrystal structures. In one example, the domains are all diamond-cubicsilicon (e.g., having a lattice constant of 5.431 Å). In anotherexample, the domains include a diamond-cubic silicon and adiamond-hexagonal silicon. In still another example, the domains includea diamond-cubic silicon and amorphous silicon. In yet still anotherexample, the domains include a diamond-cubic silicon, adiamond-hexagonal silicon, and amorphous silicon.

Another embodiment is a process that includes repeatedly applyingsufficient shear forces to silicon metal in the presence of an admixtureof an alkane and an alkene thereby mechanochemically functionalizing thesilicon and providing a functionalization on the surface of the silicon.In this embodiment, the shear forces are applied to the silicon in thepresence of the alkane and the alkene until the silicon metal is reducedto a plurality of functionalized silicon nanoparticles. In one instance,the functionalization on the silicon surface is an admixture of analkane-functionalization (derived from the alkane) and analkene-functionalization (derived from the alkene).

In another instance, the alkane can have a molecular formula ofC_(x)H₂x₊₂ wherein x is in the range of 4 to about 25. Preferably, x isin the range of 5-20, more preferably in the range of 6-18, and evenmore preferably in the range of 6-12. Herein, the alkane can be liner(n-alkane), branched (single or multiple branches), cyclic, or acombination thereof. In one preferable example, the alkane is linear. Inanother preferable example, the alkane is branched.

In still another instance, the alkene can have a molecular formula ofC_(x)H₂x wherein x is in the range of 5 to about 25. Preferably, x is inthe range of 6-20, more preferably in the range of 6-18, and even morepreferably in the range of 6-12. Herein, the alkene can be liner(n-alkene), branched (single or multiple branches), cyclic, or acombination thereof. In one preferable example, the alkene is linear. Inanother preferable example, the alkene is branched.

In yet another instance, the alkene can include a heteroatomfunctionality. Preferably, the heteroatom functionality is selected froman alcohol and an amine. In other examples, the heteroatom functionalitycan be selected from an alcohol, an aldehyde, a ketone, a carboxylate,an amine, an imide, a nitrile, a cyanate, an isocyanate, a thiocyanate,an isothiocyanate, an amide, a silyl, or a mixture thereof.

In still yet another instance, the functionalized silicon nanoparticlesare polycrystalline silicon nanocrystals. As used herein, apolycrystalline silicon nanocrystal is a discrete silicon nanocrystalthat has more than one crystal domain. The domains can be of the samecrystal structure and display discontinuous domains, or the domains canbe of different crystal structures. In one example, the domains are alldiamond-cubic silicon (e.g., having a lattice constant of 5.431 Å). Inanother example, the domains include a diamond-cubic silicon and adiamond-hexagonal silicon. In still another example, the domains includea diamond-cubic silicon and amorphous silicon. In yet still anotherexample, the domains include a diamond-cubic silicon, adiamond-hexagonal silicon, and amorphous silicon.

Still another embodiment is a process that includes shearing siliconmetal and exposing a silicon surface having a Miller index other than a(111) plane or a (100) plane. Notably, the impact fracture of siliconmetal (silicon crystal) by, for example, ball milling or grinding,predominately provides a silicon surface having a (111) Miller index. Inpart, this is driven by the fracture propagation in the silicon latticebeing preferential in the (111) plane. Herein, shear forces are appliedto the silicon surface and these forces provide shear propagation thatis inclined relative to the (111) plane. Accordingly, the shearing ofthe silicon metal exposes silicon surfaces (shear surfaces or shearplanes) that are inclined relative to the (111) plane. In one instance,the exposed silicon surface is oriented between the (113) and (114)planes. The exposed silicon surface can have other Miller indices, andpreferentially have a plurality of exposed silicon surface that eachhave their own Miller indices. In one preferred instance, the siliconmetal has a substantial portion that exists in a diamond-cubic crystalstructure. Preferably, at least 10 atom %, 20 atom %, 25 atom %, 30 atom%, 35 atom %, 40 atom %, 45 atom %, 50 atom %, 55 atom %, 60 atom %, 65atom %, 70 atom %, 75 atom %, 80 atom %, 85 atom %, 90 atom %, or 95atom % of the silicon metal has a diamond-cubic crystal structure.Notably, the silicon metal can be single crystalline or can bepolycrystalline. Additionally, the silicon metal can include alloyingelements as long as the crystal structure maintains a substantialportion of diamond-cubic structure.

As a product of the shearing, the exposed silicon surface will carry atleast one silicon radical. That is, the silicon metal that makes up thesilicon surface will include at least one silicon radical, preferably,the silicon surface will carry a plurality of silicon radicals. Morepreferably, the as herein provided silicon radical is of sufficientenergy to react with an alkane. That is, the silicon radical hassufficient energy to break a H—C or a C—C bond of an alkane.

This process further includes mechanochemically functionalizing thesilicon surface by reacting the silicon radical with an organic coatingagent. The reaction with the organic coating agent, preferably,covalently bonds the organic coating agent to the silicon surface (e.g.,though a Si—C sigma bond).

In one instance, the organic coating agent is selected from an alkane,an alkene, an alkyne, an arene, an alkyl halide, an aryl halide, analdehyde, a ketone, an ester, an amide, an amine, and a nitrile. Inanother instance, the organic coating agent is an admixture of at leasttwo different compounds, each individually selected from an alkane, analkene, an alkyne, an arene, an alkyl halide, an aryl halide, analdehyde, a ketone, an ester, an amide, an amine, and a nitrile. Herein,the general classifications of the organic coatings agents furtherinclude combinations thereof. For example, the alkene and the alkylhalide classifications, each, include 8-chloro-octene. In one instance,the organic coating agent includes an alkane. In another instance, theorganic coating agent consists essentially of an alkane. In yet anotherinstance, the organic coating agent includes an alkene, an alkyne, or anaryl. In yet still another instance, the organic coating agent is freeof a hydroxyl (—OH) functionality, i.e. the organic coating agent ispreferably free of any alcohol. In another instance, the organic coatingagent is free of hydroxyl and ether functionalities. In still yetanother instance, the organic coating agent is free of any functionalitythat includes an oxygen atom.

Furthermore, the reaction of the silicon radical with the organiccoating agent provides an organic radical (e.g., by extraction of ahydrogen atom for the organic coating agent, by the cleavage of a C—Cbond in the organic coating agent, or by the reaction of an unsaturatedfunctionality, for example an alkene, and the migration of the radicalto a position on the organic coating agent). The organic radical, eithercarried on the silicon surface or within a reaction solution, ispreferably, thereafter, quenched. The quenching can be, for example, bythe reaction with other reagents within the reaction solution (e.g., byhydride extraction from another moiety) or by further reaction with thesilicon surface.

Preferably, the silicon metal is repeatedly (e.g., continuously) shearedin the presence the organic coating agent until the silicon metal isreduced to a plurality of functionalized silicon nanoparticles. Herein,the functionalized silicon nanoparticles include an organic coatingfunctionality covalently bound to the silicon surface. As used herein,the organic coating functionality is understood to include the radicaladdition of the organic coating agent to the silicon surface and thequenching of any resultant organic radical and/or a portion of theorganic coating agent bound to the silicon surface (e.g., by the radicalreaction of the organic coating agent with the silicon surface or by theaddition of an organic radical with a silicon radical). Preferably, theplurality of functionalized silicon nanoparticles having a d₉₀ of lessthan about 350 nm, less than about 300 nm, or, more preferably, lessthan about 250 nm.

Yet another embodiment is a material that includes a plurality ofsilicon nanoparticles each carrying an alkyl-functionalization derivedfrom an alkane. As used herein, the alkyl-functionalization can have amolecular formula of C_(x)H₂x₊₁ (wherein the alkane has a molecularformula of C_(x)H₂x₊₂) wherein x is in the range of 4 to about 25.Preferably, x is in the range of 5-20, more preferably in the range of6-18, and even more preferably in the range of 5-12 or 6-12. Herein, thealkyl-functionalization can be liner, branched (single or multiplebranches), cyclic, or a combination thereof. In one preferable example,the alkyl-functionalization is linear. In another preferable example,the alkyl-functionalization is branched. Still further, thealkyl-functionalization can have a non-specific chain length andorientation on the silicon surface. That is, the alkyl-functionalizationcan have a molecular formula of C_(x)H₂x₊₁ where x is not a singleinteger but is a range of integers from 1 to about 25 in those exampleswhere the alkane had a molecular formula wherein x ranged up to 25. Ininstances wherein the silicon nanoparticles carryalkyl-functionalizations, each silicon nanoparticle can further carry ahydride functionalization (e.g., the silicon surface carries both alkyland hydride groups bound to silicon atoms).

In one instance, the silicon nanoparticles include polycrystallinesilicon nanocrystals. As used herein, a polycrystalline siliconnanocrystal is a discrete silicon nanocrystal that has more than onecrystal domain. The domains can be of the same crystal structure anddisplay discontinuous domains, or the domains can be of differentcrystal structures. In another instance, the silicon nanoparticlesinclude silicon nanocrystals having dislocated diamond-cubic crystalstructures. In still another instance, the silicon nanoparticles includesilicon nanocrystals having diamond-cubic and diamond-hexagonal crystalstructures. In still yet another instance, the silicon nanoparticlesinclude silicon nanocrystals each having a plurality of crystal domains.

In another instance, the plurality of silicon nanoparticles has a d₉₀ ofless than about 350 nm. Herein, the d₉₀ is the size distribution of thenanoparticles wherein for d₉₀ 90% of the particles have a size smallerthan the represented value. Herein, the d₉₀ can be or be less than about350 nm, 300 nm, 250 nm, or 200 nm.

In still another instance, each silicon nanoparticle further carries afunctionalization derived from an alkene. Typically, thefunctionalization derived from an alkene has the same molecular formulaas the alkene, for example a functionalization derived from octene(C₈H₁₆) bridges two neighboring silicon atoms on the surface and thefunctionalization has the formula C₈H₁₆. The functionalization derivedfrom the alkene can have a molecular formula of C_(x)H₂x wherein x is inthe range of 5 to about 25. Preferably, x is in the range of 6-20, morepreferably in the range of 6-18, and even more preferably in the rangeof 6-12. Herein, the functionalization derived from the alkene can beliner, branched (single or multiple branches), cyclic, or a combinationthereof. In one preferable example, the functionalization derived fromthe alkene is linear. In another preferable example, thefunctionalization derived from the alkene is branched. In yet anotherinstance, the functionalization derived from the alkene can include aheteroatom functionality. Preferably, the heteroatom functionality isselected from an alcohol and an amine. In other examples, the heteroatomfunctionality can be selected from an alcohol, an aldehyde, a ketone, acarboxylate, an amine, an imide, a nitrile, a cyanate, an isocyanate, athiocyanate, an isothiocyanate, an amide, a silyl, or a mixture thereof.

In still yet another instance, each silicon nanoparticle further carriesa functionalization derived from an alkyne. Typically, thefunctionalization derived from an alkyne has the same molecular formulaas the alkyne, for example a functionalization derived from octyne(C₈H₁₄) bridges two neighboring silicon atoms on the surface and thefunctionalization has the formula C₈H₁₄. The functionalization derivedfrom the alkyne can have a molecular formula of C_(x)H₂x⁻² wherein x isin the range of 5 to about 25. Preferably, x is in the range of 6-20,more preferably in the range of 6-18, and even more preferably in therange of 6-12. Herein, the functionalization derived from the alkyne canbe liner, branched (single or multiple branches), cyclic, or acombination thereof. In one preferable example, the functionalizationderived from the alkyne is linear. In another preferable example, thefunctionalization derived from the alkyne is branched. In yet anotherinstance, the functionalization derived from the alkyne can include aheteroatom functionality. Preferably, the heteroatom functionality isselected from an alcohol and an amine. In other examples, the heteroatomfunctionality can be selected from an alcohol, an aldehyde, a ketone, acarboxylate, an amine, an imide, a nitrile, a cyanate, an isocyanate, athiocyanate, an isothiocyanate, an amide, a silyl, or a mixture thereof.

Herein, shear force or shear forces can be applied to the silicon metalby the application of a mill, mixer, or grinder that is capable of thehigh shearing mixing/milling of the silicon metal. Mechanical shearingmethods may employ homogenizers, extruders, injection molding machines,roller blade mixers, Banbury® type mixers, Brabender® type mixers,pin-mixers, rotor/stator mixers, and the like. In one instance, shearingcan be achieved by introducing the silicon and alkane at one end of anextruder (single or double screw) and receiving the sheared material atthe other end of the extruder. The temperature of the materials enteringthe extruder, the temperature of the extruder, the concentration ofmaterials added to the extruder, the amount of solvent (alkane) added tothe extruder, the length of the extruder, residence time of thematerials in the extruder, and the design of the extruder (single screw,twin screw, number of flights per unit length, channel depth, flightclearance, mixing zone, etc.) are several variables which control theamount of shear applied to the materials. In another instance, shearingcan be achieved by passing an admixture of the silicon metal and alkanethrough a rotor-stator (e.g., a rotor-stator mixer, a rotor-statorhomogenizer, or a rotor-stator mill). The rotor-stator can employ apin-mill design, a conical pass designs, disk design, or the like. Insome instances, the rotor-stator can include a bead mill. Notably, theapplication of the shear force(s) can be accomplished as a batch, asemi-batch, or a circulating flow, or a continuous flow process.

As used herein, the processes and products are described relative tosilicon metal. In one example, the silicon metal is analytically puresilicon, for example, single crystal silicon (e.g., platters) used inthe semiconductor/computer industry. In another example, the siliconmetal is recycle or scrap from the semiconductor or solar industries. Instill another example, the silicon metal is a silicon alloy. A siliconalloy can be a binary alloy (silicon plus one alloying element), can bea tertiary alloy, or can include a plurality of alloying elements. Thesilicon alloy is understood to be a majority silicon. A majority siliconparticle means that the metal has a weight percentage that is greaterthan about 50% (50 wt. %) silicon, preferably greater than about 60 wt.%, 70 wt. %, 80 wt. %, 90 wt. %, or 95 wt. % silicon; these can includesilicon alloys that comprise silicon and at least one alloying element.The alloying element can be, for example, an alkali metal, analkaline-earth metal, a Group 13 to 16 element, a transition element, arare earth element, or a combination thereof, but not Si. The alloyingelement can be, e.g., Li, Na, Mg, Ca, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr,Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd,B, Al, Ga, In, Ge, Sn, P, As, Sb, Bi, S, Se, Te, or a combinationthereof. In one instance, the alloying element can be lithium,magnesium, aluminum, titanium, vanadium, chromium, manganese, iron,cobalt, nickel, copper, or a mixture thereof. In another instance, thesilicon alloy can be selected from SiTiNi, SiAlMn, SiAlFe, SiFeCu,SiCuMn, SiMgAl, SiMgCu, or a combination thereof.

In still another example, the herein described processes and productscan utilize germanium and/or indium, without or without silicon.Accordingly, the processes and products describe above can be include Geor In in replacement of the Si. Still further, the processes andproducts can utilize alloys of Ge or In.

EXAMPLES Non-Shear Example

Silicon metal was processed for 12 hours in a high-energy ball mill inaccordance to the descriptions provided in U.S. Pat. No. 7,883,995. Thenon-shear product was analyzed by FTIR, SEM, and TEM. The non-shearproduct showed no alkane functionalization of the silicon metal.

High-Shear Example

A silicon metal feed stock was prepared from silicon wafer (singlecrystal) by pre-crushing and sieving the silicon metal to less than 250μm. Then 250 g of the sieved silicon metal and about 1000 g of n-hexanewere admixed and the silicon continuously suspended in the n-hexane byapplication of a paddle-type (non-shear) mixer. The suspension wasrecirculated through a rotor-stator mill for 3-6 hours. Aliquots wereremoved about every 30 min and the particle size was determined. Afterthe silicon is reduced to nanoparticles, the slurry was removed from therotor-stator system and the hexane evaporated. The resulting product wasprocessed to provide a free-flowing powder and then dried in a vacuumoven. This high-shear product was analyzed by FTIR, SEM, and TEM. Thehigh-shear product showed alkane functionalization on the silicon and adifferent morphology by SEM and TEM.

While the compositions and methods of this invention have been describedin terms of preferred embodiments, it will be apparent to those of skillin the art that variations may be applied to the compositions and/ormethods in the steps or in the sequence of steps of the method describedherein without departing from the concept, spirit and scope of theinvention. More specifically, it will be apparent that certain agentsthat are both chemically and physically related may be substituted forthe agents described herein while the same or similar results would beachieved. All such similar substitutes and modifications apparent tothose skilled in the art are deemed to be within the spirit, scope andconcept of the invention as defined by the appended claims.

What is claimed:
 1. A process of mechanochemically functionalizingsilicon nanoparticles with an alkane, comprising: shearing silicon metalin the presence of an alkane by applying shear forces to the siliconmetal to expose a sheared silicon surface, the alkane having a molecularformula of C_(x)H_(2x+2) where x is in the range of 4 to about 25,forming an alkyl-functionalization on the sheared silicon surface; andcontinuing to shear the silicon metal in the presence of the alkaneuntil the silicon metal is reduced to a plurality of functionalizedsilicon nanoparticles.
 2. The process of claim 1, wherein shearing thesilicon metal exposes silicon radicals on the sheared silicon surface,the process then including reacting the silicon radicals with the alkaneto provide the alkyl-functionalization.
 3. The process of claim 2,further comprising fracturing the silicon metal to expose siliconradicals on a fractured silicon surface.
 4. The process of claim 1,wherein the plurality of functionalized silicon nanoparticles have a d₉₀of less than about 350 nm.
 5. A process comprising: repeatedly applyingsufficient shear forces to silicon metal in the presence of an admixtureof an alkane and an alkene thereby mechanochemically functionalizing thesilicon and providing a functionalization on the surface of the silicon,the alkane having a molecular formula of C_(x)H_(2x+2) where x is in therange of 4 to about 25, the alkene having a molecular formula ofC_(x)H_(2x) where x is in the range of 5 to about 25; and continuing toapply the shear forces to the silicon in the presence of the alkane andthe alkene until the silicon metal is reduced to a plurality offunctionalized silicon nanoparticles.
 6. The process of claim 5, whereinthe functionalization on the silicon surface is an admixture of analkane-functionalization and an alkene-functionalization.
 7. The processof claim 5, wherein the functionalized silicon nanoparticles arepolycrystalline silicon nanocrystals.
 8. A process comprising: shearingsilicon metal thereby exposing a silicon surface having a Miller indexother than a (111) plane or a (100) plane, the silicon surface carryingat least one silicon radical; where the silicon radical is of sufficientenergy to react with an alkane; mechanochemically functionalizing thesilicon surface with a Si—C sigma bond.
 9. The process of claim 8,wherein at least 25 atom % of the silicon metal has a diamond-cubiccrystal structure.
 10. The process of claim 8, wherein mechanochemicallyfunctionalizing the silicon surface with a Si—C sigma bond includereacting the silicon radical with an organic coating agent and formingan organic radical, thereafter quenching the organic radical.
 11. Theprocess of claim 8, wherein the process comprises: repeatedly shearingthe silicon metal, thereby repeatedly exposing a plurality of siliconradicals on a plurality of silicon surfaces and mechanochemicallyfunctionalizing the silicon surfaces with Si—C sigma bonds, and therebyreducing the silicon metal to a plurality of functionalized siliconnanoparticles.
 12. The process of claim 11, wherein mechanochemicallyfunctionalizing the silicon surfaces with Si—C sigma bonds includesreacting the silicon radicals with an alkane having a molecular formulaof C_(x)H_(2x+2) where x is in the range of 4 to about
 25. 13. Theprocess of claim 12, wherein mechanochemically functionalizing thesilicon surfaces with Si—C sigma bonds consists essentially of reactingthe silicon radicals with the alkane.
 14. The process of claim 11,wherein the plurality of functionalized silicon nanoparticles having ad₉₀ of less than about 350 nm.
 15. The process of claim 14, wherein thed₉₀ is less than about 300 nm.
 16. The process of claim 15, wherein thed₉₀ is less than about 250 nm.